As a conventional detection device for side collision of a vehicle is proposed a detection device disclosed in, for example, JP-A-H05-93735 (patent document 1, which corresponds to U.S. Pat. No. 5,281,820). When the detection device for side collision of a vehicle, which is disclosed in the patent document 1, detects the deformation of a reinforcing member arranged in the interior of a side door, the detection device determines that collision requiring the protection of a passenger occurs. Here, an outer plate is very low in bending rigidity, so that the outer plate is easily deformed by a small impact. For this reason, for example, in a case where when a side door is opened, the side door is bumped against an electric pole or the like to deform an outer plate or in a case where an outer plate is deformed by a small impact while a vehicle is running, an air bag or the like does not need to be developed. In other words, when the air bag or the like is developed by detecting the deformation of the outer plate, the air bag is developed also in the above-mentioned cases. Thus, according to the construction of the patent document 1, even when an outer plate is deformed, if an impact is such a small level of impact that does not deform an reinforcing member, it is determined that a vehicle does not collide with an object. Thus, it is possible to detect only collision requiring the protection of a passenger and to develop an air bag or the like only in the case of the collision.
To know the extent to which the above-mentioned reinforcing member is brought close to the interior of a vehicle compartment (that is, to a passenger side) when the vehicle undergoes collision such as side collision becomes a guideline at the time of determining the degree of seriousness of the collision. However, although the detection device for side collision of a vehicle described in the patent document 1 can detect whether or not the reinforcing member is deformed, the detection device cannot clearly find the extent to which the reinforcing member is actually brought close to the interior of the vehicle compartment by the deformation of the reinforcing member. For example, even when the reinforcing member is deformed, the direction in which the reinforcing member is deformed is not always pointed inside the vehicle compartment. Moreover, for example, even when the reinforcing member is deformed inward of the vehicle compartment, if the vehicle compartment is moved in a direction in which the reinforcing member is deformed to an extent equal to or more than the deformation of the reinforcing member, the reinforcing member is not brought closer to the vehicle compartment.
Further, the detection device for side collision of a vehicle described in the patent document 1 detects collision only when a portion, which has a sensor arranged thereon, of the reinforcing member or a portion, which is closest to the sensor, of the reinforcing member is deformed, so that the detection range of the sensor becomes very narrow or a pinpoint of detection. Thus, the detection device has the problem of detecting only collision at a specified position. If it is intended to make a detection device detect collision in a wide range, a very large number of sensors need to be fixed to the reinforcing member, which causes the problem of increasing a space for arranging the sensors and the problem of complicating the arrangement of the sensors.
Still further, in the detection device for side collision of a vehicle, described in the patent document 1, as for the structure of fixing a detection sensor to a side door, the detection sensor is fixed to an inner plate side via a support member fixed to the inner plate in such a way as to be close to the reinforcing member. The detection sensor is arranged on the inner plate side with respect to the reinforcing member, and when an object collides with the side door, the reinforcing member is deformed to the inner plate side, so that the detection sensor receives an impact caused by the deformation of the reinforcing member, thereby being operated. With this, the detection device for side collision of a vehicle can detect that an object collides with the vehicle on the basis of a detection signal sent by the detection sensor. Here, an impact sensor or an electric coil is used as the detection sensor.
However, a space for opening or closing the door glass of the side door in the up and down direction is interposed between the reinforcing member and the inner plate. A stay for fixing and driving up and down the door glass is disposed on the lower side of the door glass, and when the door glass is opened or closed, the stay is moved up and down. Thus, it is difficult to arrange the detection sensor in a range in which the door glass and the stay are moved up and down according to the method described in the patent document 1. When the detection sensor is arranged at a position in which the detection sensor does not interfere in terms of space with the stay, a position in which the detection sensor is arranged is limited to positions in the front direction and in the rear direction of the vehicle of the side door, which presents the problem of making it difficult to detect collision in a wide range in the front and rear direction of the vehicle of the side door.
Further, the above-mentioned detection device for side collision of a vehicle detects collision only when the position of the reinforcing member having the sensor arranged thereon is displaced, so that the range of detection of the collision becomes very narrow. Thus, there is presented a problem that the detection device can detect only collision at a specified position.
Still further, as another conventional detection device for side collision of a vehicle is proposed a detection device disclosed in, for example, JP-A-H07-186878 (patent document 2). The detection device for side collision of a vehicle disclosed in the patent document 2 is constructed of: two cantilever beams; and plural sensors for detecting side collision. The two cantilever beams are arranged between the outer plate and the inner plate of the side door in parallel in the front and rear direction of the vehicle in a state where their fixing end portions are fixed to the inner plate. The sensors for detecting side collision are sensors turned on when they are pressed, and the sensors are arranged at specified intervals on the outer plate of the side door of the cantilever beams. When an object collides with the side door, the outer plate is depressed to the inner plate side to press the sensors for detecting side collision, which are arranged on the cantilever beams, whereby the sensors for detecting side collision are turned on. In this manner, it is possible to detect that the object collides with the vehicle.
However, the conventional detection device for side collision of a vehicle employs a complex mechanical construction having two cantilever beams, so that the conventional detection device becomes very large in size, which presents a problem in the space for arranging the detection device. In particular, a recent vehicle has other equipment such as a speaker and a power window mechanism arranged in the interior of the side door thereof, so that it is very important to ensure a space in the interior of the side door.